1 // Part 1

     2 

     3 

     4 //(1)

     5 def collatz(n: Long): List[Long] =

     6   if (n == 1) List(1) else

     7     if (n % 2 == 0) (n::collatz(n / 2)) else 

     8       (n::collatz(3 * n + 1))

     9 

    10 // an alternative that calculates the steps directly

    11 def collatz1(n: Long): Int =

    12   if (n == 1) 1 else

    13     if (n % 2 == 0) (1 + collatz1(n / 2)) else 

    14       (1 + collatz1(3 * n + 1))

    15 

    16 

    17 //(2)

    18 def collatz_max(bnd: Int): Int = {

    19   (for (i <- 1 to bnd) yield collatz(i).length).max

    20 }

    21 

    22 

    23 val bnds = List(10, 100, 1000, 10000, 100000, 1000000, 10000000)

    24 

    25 for (bnd <- bnds) {

    26   val max = collatz_max(bnd)

    27   println(s"In the range of 1 - ${bnd} the maximum steps are ${max}")

    28 }

    29